1. Field of the Invention
The present invention relates generally to the field of fluid control valves; and, more particularly, to a retrofit second packing chamber for quarter-turn valves to assist manufacturers and end users of process equipment in meeting new, more stringent requirements regarding the control of fugitive emissions.
2. Description of the Prior Art
Valves are commonly used in industry to restrict, divert, or blend flows of fluids. Most valves have the problem of sealing the valve stem or shaft used to transmit actuator motion from outside the valve to the closure member (which may be a plug, disc, ball, gate, etc.) inside the pressurized zone of the valve. Valve stems are typically sealed through a packing chamber (stuffing box) and/or a bellows-type seal. The design of such seals varies greatly depending on the style and type of valve, the particular application in which the valve is to be used and the manufacturer.
One particularly popular type of valve is referred to as a quarter-turn valve. Quarter-turn valves include valves of the ball, butterfly and plug types, etc., and open and close with a one-quarter turn rotation of the valve stem.
Quarter-turn valves are used in numerous applications. Some applications require that the valve be operated infrequently, while other applications require that the valve be used frequently on a regular basis. Such valves may also be used under conditions in which pressures may range from a vacuum to in excess of 5000 psig, and in which temperatures may range from cryogenic to greater than 1500.degree. F.
Irrespective of the application of the valve, the general concept of compressing a deformable sealing material or packing between the wall of the packing chamber and the valve stem to seal around the valve stem is consistent. Most packing chambers can be relatively easily adjusted to obtain an adequate seal when the valve is new. As the packing ages, however, it wears and leakage eventually tends to occur. As the packing wears, the packing chamber can usually be adjusted to apply increased pressure to the packing to reduce leakage. In time, however, the packing may harden to the point that further adjustment becomes impossible, and the packing must then be replaced.
As a result of increasing worldwide concern about the presence of noxious, toxic and hazardous compounds in the atmosphere, legislation is now in place or is being proposed in most industrialized nations of the world focusing on volatile hazardous air pollutants and volatile organic compound emissions. For example, in the United States, the 1990 Clean Air Act Amendments define 189 chemicals for which leakage to the atmosphere is considered fugitive emissions; and new regulations are being proposed which will severely limit permissible emissions of such chemicals. Such regulations will have a major impact on users of process valves, and many current valves on the market simply do not meet the stringent requirements of the proposed new legislation. Such valves will have to be replaced or otherwise modified to meet such requirements at substantial cost to manufacturers and end users of process equipment incorporating such valves.